It is common practice to make inorganic fibers, such as glass fibers, by either feeding molten glass, or glass in another form such as marbles, to a refractory bushing that is maintained at a temperature above the melting point of the inorganic material in a conventional manner. The molten inorganic material is then exuded from small orifices in the bushing to form continuous fibers. The fibers can be drawn out and are then cooled below their softening point very quickly after leaving the orifices. Glass fibers made in this manner are used to make textiles and as reinforcement for plastics in the manufacture of a variety of items such as boats, car bodies, etc.
The bushings used in these processes must be refractory because of the high temperatures involved and usually are made of a noble metal such as platinum or an alloy thereof, e.g. platinum-rhodium, platinum-palladium, etc. Normally the bottom of the bushing contains many orifices, for example, 500 to several thousand, in a small area. The refractoriness of these bushings and the precise way in which they must be made make the bushings very expensive.
Normally a bushing lasts from 4 to 8 months of continuous operation. However, occasionally a tip will become clogged with one or more particles sluffed off of the melting furnce walls, from unmelted batch, stones, or other sources. A clogged tip usually is clogged to the extent that it will no longer produce a continuous fiber, but instead drips and these drips cause breakouts which interrupt the process. Heretofore several methods have been tried to clear out the clogged tips or to close them off. These include: (1) increasing the bushing orifice section temperature to melt or boil out the obstruction, (2) heating the exterior of the obstructed tip with a torch or other means to melt out the obstruction, (3) probing up into the orifice with a small rod or wire to clear the obstruction, and (4) pinching the tip to close the orifice. None of these techniques have worked successfully. Instead it has been necessary to remove the bushing, sometimes after only a few hours of service, and replace it with a new bushing. Once the bushing is removed is must be cleaned, usually by leeching with acid to remove the solidified glass therein, and melted down for use in making new bushings. Thus, the problem of clogged tips is an expensive problem that has plagued industry for a long time.